Windows Azure媒体服务的幕后:案例研究

基于云的流媒体和制作服务对任何大型广播公司来说都是一个福音, 提供规模, power, and features inaccessible from on-premises facilities with minimal capital expenditure (CAPEX) and maintenance expenditures. 微软的IIS媒体服务, 长期以来是许多广播公司和大型企业内部部署服务器的主要内容, 已经迁移到云端，现在以 Windows Azure媒体服务. In this article, I’ll discuss the features of the service, how it was proven during the 2012年伦敦奥运会以及两个早期采用者所带来的好处， nbc环球 and the 欧洲之行 (高尔夫赛事).

了解Azure媒体服务

Windows Azure媒体服务 is the “cloud-ification” of multiple features of Microsoft’s Media Platform, 以及各种媒体合作伙伴提供的技术, many of which were critical to the London Olympics and successful results achieved by NBC and the 欧洲之行. Azure Media Services supports on-demand (currently) and live streaming (in private preview), 以及动态包装, 哪一种是HLS和平滑流格式之间的实时转换, DASH也在路上(稍后会详细介绍).

Azure还在摄取到交付的工作流程中提供多种服务, 包括编码, 内容保护, 和货币化. Azure will not completely replace Microsoft’s existing on-premises offerings such as Windows Media Services or IIS Media Services, and enterprises considering making the switch should evaluate the distinctions closely. Perhaps the biggest sticking point mitigating against moving to Azure is the inability to transmit via IP Multicast, 哪些是有效的内部网流的关键.

图1 provides a high-level schematic of the features offered by Azure Media Services; let’s start with a high-level review of its components.

图1. Windows Azure媒体服务提供的高级功能示意图

概述

与所有大型云服务一样, 虽然有些功能可以通过网络用户界面使用, 您可以通过REST API控制所有Microsoft和合作伙伴提供的特性. 微软也提供 .. NET和Java软件开发工具包(sdk)，可在 GitHub.com因为许多企业和广播开发人员都熟悉这些语言.

交付, 微软为许多设备和平台提供了客户端播放器sdk, including Flash (using Adobe open source media framework; OSMF), iOS, Android, 联网电视和机顶盒等设备, 以及Windows 8, Silverlight, Xbox, 和Windows Phone (图2). 在高水平上, 这些sdk和播放器框架使设备能够播放MPEG-DASH, 光滑的流, HLS格式文件, 或MP4文件通过渐进式下载传送. sdk和播放器框架支持对视频播放的广泛控制, 包括广告插入和数字版权管理(DRM), 提供玩家样本以帮助开发者快速上手和运行.

图2. 向微软和非微软端点的交付选项

PRICING

与所有基于云的服务一样, Azure的定价因使用情况而异, 计算时间单独收费, 预留计算时间, 存储, 出站数据(但不包括入站数据), 使用的服务. The base charge for media services is calculated on the amount of encoded throughput, 其中包括入站和出站数据. 价格取决于使用情况，即付即用的价格从1美元起.每GB数据99美元, with volume and commitments dropping that down as low as 69 cents per GB on the price sheet; it’s lower for higher negotiated volumes.

在基本计划中，编码是串行执行的. 如果你需要更快的编码, 您可以启动将并行编码的其他编码器, 你要按24小时计费. 除了, 如果您选择使用动态包装, 后面会进一步解释, 你必须预留额外的原始容量, 每月199美元，最高200Mbps的带宽容量.

这一切都从摄入开始

用于视频点播(VOD), Azure媒体服务提供了多种摄取选项, including the ability to upload files over HTTP or HTTPS with advanced encryption standard (AES)-256 encryption, 哪一种适合每天少量上传. 对于较大的上传，您可以使用Bulk Ingest .NET Library or a partner solution such as Aspera On Demand for Microsoft Windows Azure, 在Windows Azure云上运行Aspera传输服务器软件. 这些传输是安全的，并利用了aspa的专利快速传输技术, 它可以显著加快通过FTP和HTTP的传输时间.

对于已经在Azure中存储内容的生产者, Microsoft also supports “blob to blob” transfers and 存储 account to 存储 account transfers. 最后, 对于小工作, you can also upload files less than 200MB in size directly via controls provided in the Windows Azure Portal.

编码和格式转换

用于编码和格式转换, Microsoft has migrated two on-premises tools to the cloud: Expression Encoder (encoding) and Transform Manager (format conversion), although these tools will be supplemented by cloud-based versions of third-party encoders in the future. 在工作流程方面, 表达式编码器的Azure版本, 现在被称为Windows Azure媒体编码器, 能输入多种格式吗, 使用ProRes格式的QuickTime文件除外, 微软将这一赤字归因于苹果缺乏云许可, 尽管其他几个基于云的编码器与ProRes兼容.

编码器可以输出单个Windows Media Video (WMV)或多个, 符合共和党的MP4文件, or encode either format into the 光滑的流 file format for adaptive delivery (Protected Interoperable File Format; PIFF 1.1). 创建后，无论是MP4文件还是H.264编码的平滑文件可以转换成HLS格式交付到iOS, via either the Azure version of Transform Manager (called the Windows Azure Media Packager) or by the aforementioned dynamic packaging feature (图3). 微软已经演示了DASH支持，应该很快就可以使用. [编者注:自本文撰写之日起, Microsoft has introduced a preview feature of Program Manager for Dynamic Packaging that enables support for MPEG-DASH live profile streaming. 阅读更多 here.]

图3. 动态打包节省了存储和编码成本.

The key benefits of dynamic packaging are reduced 存储 and transcoding costs -- you only have to encode and store one set of files to deliver to multiple formats. Offsetting this is the cost of reserved origin units that you have to lease at $199 per month per unit.

动态打包也有一些限制. First, it’s transmux only; it will not transcode a single file into multiple iteration -- you’d have to do that first. 动态打包也不适用于加密的内容, 虽然这应该在2013年底可用. 直到动态封装可以处理加密, 如果您需要为Smooth和HLS加密内容, 您必须创建两组独立的文件, 应用AES 128位加密HLS和PlayReady平滑流文件.

Note that neither RTMP or HTTP-based Dynamic Streaming is supported as an output format, 直接在Azure Media Encoder中, 或通过Azure Media Packager或动态打包. 访问Flash客户端, Azure users would have to build a Flash client using the OSMF with 光滑的流 plug-in, or use products such as JW Player to incorporate HLS playback into Flash-enabled computers.

Azure媒体服务和奥运会

Microsoft has a long history of debuting and proving its products in large-scale events, 就像2008年夏季奥运会上的流畅流一样. 2012年伦敦奥运会, Microsoft proved the robustness of its own cloud-based components and those offered by third-party partners, 从而产生了真正的服务，而不仅仅是各部分的总和.

首先是数字. 在伦敦, Azure媒体服务交付了超过2个,300 hours of live and VOD HD content to more than 20 countries for multiple Olympics broadcasters, 包括法国, 报道(西班牙), CTV(加拿大), 泰拉(中美洲和南美洲).

在工作流程方面, 微软从奥林匹克广播公司获得了1080i信号, 哪个被压缩到17个.7Mbps使用H.264编解码器和MPEG-2传输流包装器和多播到多个公司. 从那里, 流被转码成八个不同的文件, 范围从150Kbps (336x192分辨率)到3.45Mbps (1280x720) and published to multiple Windows Azure data centers for fault tolerance. 从那里，Akamai的高清网络传送流. 一旦直播完成, they were immediately available for replay during and after the live event via a DVR feature -- no additional transcoding was necessary.

平滑流是H的通用自适应格式.264和AAC文件. 在电脑上, 流被传送给Silverlight玩家供本地消费, and they were played in Flash via a native ActionScript SDK developed with Canadian developer gskinner.com. 另一个开发人员, deltatre, created an iPhone and iPad player using the iOS 光滑的流 SDK developed by Microsoft, and an Android player using a 光滑的流 SDK for Android developed by NexStreaming.

Most of these features could have been duplicated by racks of on-premises encoders and servers, 虽然成本和设置时间会让人望而却步. One feature that couldn’t be easily duplicated via on-premises equipment was cloud-based editing. 多家广播公司参与其中, the Microsoft team needed to provide a solution that would enable the fast editing of newly captured footage for traditional and online broadcast without first downloading all the files to local 存储.

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